1. Chp 13
Sound and Music

2. What is sound?
A sound wave is a wave of alternating high pressure and low pressure regions.
Anything that vibrates in air creates a sound wave.
It is a longitudinal wave because the air compresses in the direction of travel

3. Loudness The loudness of a sound is measured in decibels (dB)
The louder the sound the higher the amplitude of the wave

4. Decibel Scale The decibel scale is a logarithmic measure of sound.
An increase of 20 dB means the wave has a 10 times greater amplitude
But, our ears perceives a 20 dB increase to be about twice as loud

5. Frequency of Sound
We hear the different frequencies of sound has having a different pitch.
Low frequency has a low pitch
High frequency has a high pitch
Humans can hear from about 20 Hz to 20,000 Hz
Human ears are most sensitive for sounds between 100 and 2,000 Hz (range of speech)

6. Wavelength
The frequency and wavelength of sound are inversely related.
When frequency goes up, wavelength goes down.

7. Speed of Sound
The speed of sound depends upon the material the sound is traveling.
Sound travels faster in a solid than in air.
Sound requires a medium to travel. As a result, sound DOES NOT travel in a vacuum.

8. Beats
Beats – when two frequencies are close, but not exactly the same, the resulting sound seems to oscillate
When the two waves are in phase, the sound gets louder. When the two waves are out of phase, the sound gets softer

9. Music
The same note sounds different when played on different instruments.
Instruments produce a mixture of different frequencies.